avrcp: Fix compilation errors due to unaligned memory access

avrcp: Fix compilation errors due to unaligned memory access

This fix following build errors on ARM.

  CC     audio/bluetoothd-avrcp.o
audio/avrcp.c: In function avrcp_handle_get_element_attributes:
audio/avrcp.c:667:25: error: cast increases required alignment of
	target type [-Werror=cast-align]
audio/avrcp.c:690:20: error: cast increases required alignment of
	target type [-Werror=cast-align]
cc1: all warnings being treated as errors
make[1]: *** [audio/bluetoothd-avrcp.o] Error 1
make: *** [all] Error 2